docs: def get(cls, key, default=None, separator='.', global_=False):
          """ Retrieve a key value from loaded configuration.
  
          Order of search if global_=False:
          1/ environnment variables
          2/ local configuration
          3/ global configuration
          """
          # first check environnment variables
          # if we're not in global scope
          if not global_:
              ret = os.environ.get(key.upper().replace('.', '_'))
              if ret is not None:
                  return ret
  
          # then check in local and global configuration unless global_=True
          scopes = ['global'] if global_ else ['local', 'global']
          for scope in scopes:
              ret = cls._get(scope, key, default, separator)
              if ret is not None and ret != default:
                  return ret
  
          if ret is None or ret == default:
              return default